The invention relates to a magnetron sputtering cathode for vacuum coating apparatus, which has a circular target plate of the material to be sputtered, and at least one magnet system disposed in back of the target plate and consisting of two endless rows of permanent magnets, one row inside of the other, the magnets of each row having the same polarity, but the magnets of the two rows being of opposite polarity, such that over the target plate at least one endless tunnel of magnetic lines of force is formed issuing from the one row of magnets and returning to the other row of magnets, and it has a driving means for the continuous rotation of the magnet system about the central axis of the target plate.
Magnetron sputtering cathodes are characterized by a sputtering rate which is greater by a factor of 10 to 30 than sputtering systems having no magnetic field enhancement. This advantage, however, is obtained with the disadvantage of an extremely irregular sputtering of the target plate, because the pinching of the plasma, which is produced in magnetrons by the magnetic tunnel, results in a corresponding spatial limitation of the sputtering effect. The formation of a deep erosion pit, whose deepest point is situated under the culmination points of the magnetic lines of force, calls for the termination of the sputtering action after only about 25 to 30% of the target material has been sputtered. In stationary coating systems, i.e., in those in which there is no relative movement between cathode and the substrates, this would result in very irregular coating thickness. Basically, an almost photographic image of the erosion pit would be formed on the substrates.
This problem, as well as a number of attempts at its solution, is addressed in DE-OS No. 27 07 144. Such attempts at a solution also include a magnetron sputtering cathode of the kind described in the beginning, in which a single endless magnet system rotates in an eccentric position behind a circular target plate (FIGS. 22 to 25). Aside from the fact that in this case only a minuscule part of the target surface is simultaneously exposed to the sputtering (a part of the magnetron effect being thus nullified) the sputtering rate on the target surface is also very irregular, because on the one hand the time of stay under the rotating magnetic tunnel is irregular, and because on the other hand the product of the intensity of the plasma--the so-called plasma density--multiplied by the time of stay, varies in the radial direction. An irregular sputtering rate, however, results not only in an irregular ablation of the target material but also in an irregular rate of deposit on the substrates being coated which lie opposite the target surface.
The invention is therefore addressed to the task of improving a magnetron sputtering cathode of the kind described in the beginning such that the coating thickness will be made uniform on the substrates being coated.